.\" This page was taken from the 4.4BSD-Lite CDROM (BSD license)
.\"
.\" %%%LICENSE_START(BSD_ONELINE_CDROM)
.\" This page was taken from the 4.4BSD-Lite CDROM (BSD license)
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.\" @(#)xdr.3n	2.2 88/08/03 4.0 RPCSRC; from 1.16 88/03/14 SMI
.\"
.\" 2007-12-30, mtk, Convert function prototypes to modern C syntax
.\"
.TH XDR 3 2021-03-22 "" "Linux Programmer's Manual"
.SH NAME
xdr \- library routines for external data representation
.SH SYNOPSIS AND DESCRIPTION
These routines allow C programmers to describe
arbitrary data structures in a machine-independent fashion.
Data for remote procedure calls are transmitted using these
routines.
.PP
The prototypes below are declared in
.I <rpc/xdr.h>
and make use of the following types:
.PP
.RS 4
.EX
.BI "typedef int " bool_t ;
.PP
.BI "typedef bool_t (*" xdrproc_t ")(XDR *, void *,...);"
.EE
.RE
.PP
For the declaration of the
.I XDR
type, see
.IR <rpc/xdr.h> .
.PP
.nf
.BI "bool_t xdr_array(XDR *" xdrs ", char **" arrp ", unsigned int *" sizep ,
.BI "                 unsigned int " maxsize ", unsigned int " elsize ,
.BI "                 xdrproc_t " elproc );
.fi
.IP
A filter primitive that translates between variable-length arrays
and their corresponding external representations.
The argument
.I arrp
is the address of the pointer to the array, while
.I sizep
is the address of the element count of the array;
this element count cannot exceed
.IR maxsize .
The argument
.I elsize
is the
.I sizeof
each of the array's elements, and
.I elproc
is an XDR filter that translates between
the array elements' C form, and their external
representation.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_bool(XDR *" xdrs ", bool_t *" bp );
.fi
.IP
A filter primitive that translates between booleans (C
integers)
and their external representations.
When encoding data, this
filter produces values of either one or zero.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_bytes(XDR *" xdrs ", char **" sp ", unsigned int *" sizep ,
.BI "                 unsigned int " maxsize );
.fi
.IP
A filter primitive that translates between counted byte
strings and their external representations.
The argument
.I sp
is the address of the string pointer.
The length of the
string is located at address
.IR sizep ;
strings cannot be longer than
.IR maxsize .
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_char(XDR *" xdrs ", char *" cp );
.fi
.IP
A filter primitive that translates between C characters
and their external representations.
This routine returns one if it succeeds, zero otherwise.
Note: encoded characters are not packed, and occupy 4 bytes each.
For arrays of characters, it is worthwhile to
consider
.BR xdr_bytes (),
.BR xdr_opaque (),
or
.BR xdr_string ().
.PP
.nf
.BI "void xdr_destroy(XDR *" xdrs );
.fi
.IP
A macro that invokes the destroy routine associated with the XDR stream,
.IR xdrs .
Destruction usually involves freeing private data structures
associated with the stream.
Using
.I xdrs
after invoking
.BR xdr_destroy ()
is undefined.
.PP
.nf
.BI "bool_t xdr_double(XDR *" xdrs ", double *" dp );
.fi
.IP
A filter primitive that translates between C
.I double
precision numbers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_enum(XDR *" xdrs ", enum_t *" ep );
.fi
.IP
A filter primitive that translates between C
.IR enum s
(actually integers) and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_float(XDR *" xdrs ", float *" fp );
.fi
.IP
A filter primitive that translates between C
.IR float s
and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "void xdr_free(xdrproc_t " proc ", char *" objp );
.fi
.IP
Generic freeing routine.
The first argument is the XDR routine for the object being freed.
The second argument is a pointer to the object itself.
Note: the pointer passed to this routine is
.I not
freed, but what it points to
.I is
freed (recursively).
.PP
.nf
.BI "unsigned int xdr_getpos(XDR *" xdrs );
.fi
.IP
A macro that invokes the get-position routine
associated with the XDR stream,
.IR xdrs .
The routine returns an unsigned integer,
which indicates the position of the XDR byte stream.
A desirable feature of XDR
streams is that simple arithmetic works with this number,
although the XDR stream instances need not guarantee this.
.PP
.nf
.BI "long *xdr_inline(XDR *" xdrs ", int " len );
.fi
.IP
A macro that invokes the inline routine associated with the XDR stream,
.IR xdrs .
The routine returns a pointer
to a contiguous piece of the stream's buffer;
.I len
is the byte length of the desired buffer.
Note: pointer is cast to
.IR "long\ *" .
.IP
Warning:
.BR xdr_inline ()
may return NULL (0)
if it cannot allocate a contiguous piece of a buffer.
Therefore the behavior may vary among stream instances;
it exists for the sake of efficiency.
.PP
.nf
.BI "bool_t xdr_int(XDR *" xdrs ", int *" ip );
.fi
.IP
A filter primitive that translates between C integers
and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_long(XDR *" xdrs ", long *" lp );
.fi
.IP
A filter primitive that translates between C
.I long
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "void xdrmem_create(XDR *" xdrs ", char *" addr ", unsigned int " size ,
.BI "                   enum xdr_op " op );
.fi
.IP
This routine initializes the XDR stream object pointed to by
.IR xdrs .
The stream's data is written to, or read from,
a chunk of memory at location
.I addr
whose length is no more than
.I size
bytes long.
The
.I op
determines the direction of the XDR stream (either
.BR XDR_ENCODE ,
.BR XDR_DECODE ,
or
.BR XDR_FREE ).
.PP
.nf
.BI "bool_t xdr_opaque(XDR *" xdrs ", char *" cp ", unsigned int " cnt );
.fi
.IP
A filter primitive that translates between fixed size opaque data
and its external representation.
The argument
.I cp
is the address of the opaque object, and
.I cnt
is its size in bytes.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_pointer(XDR *" xdrs ", char **" objpp ,
.BI "                   unsigned int " objsize ", xdrproc_t " xdrobj );
.fi
.IP
Like
.BR xdr_reference ()
except that it serializes null pointers, whereas
.BR xdr_reference ()
does not.
Thus,
.BR xdr_pointer ()
can represent
recursive data structures, such as binary trees or
linked lists.
.PP
.nf
.BI "void xdrrec_create(XDR *" xdrs ", unsigned int " sendsize ,
.BI "                   unsigned int " recvsize ", char *" handle ,
.BI "                   int (*" readit ")(char *, char *, int),"
.BI "                   int (*" writeit ")(char *, char *, int));"
.fi
.IP
This routine initializes the XDR stream object pointed to by
.IR xdrs .
The stream's data is written to a buffer of size
.IR sendsize ;
a value of zero indicates the system should use a suitable default.
The stream's data is read from a buffer of size
.IR recvsize ;
it too can be set to a suitable default by passing a zero value.
When a stream's output buffer is full,
.I writeit
is called.
Similarly, when a stream's input buffer is empty,
.I readit
is called.
The behavior of these two routines is similar to
the system calls
.BR read (2)
and
.BR write (2),
except that
.I handle
is passed to the former routines as the first argument.
Note: the XDR stream's
.I op
field must be set by the caller.
.IP
Warning: to read from an XDR stream created by this API,
you'll need to call
.BR xdrrec_skiprecord ()
first before calling any other XDR APIs.
This inserts additional bytes in the stream to provide
record boundary information.
Also, XDR streams created with different
.BR xdr*_create
APIs are not compatible for the same reason.
.PP
.nf
.BI "bool_t xdrrec_endofrecord(XDR *" xdrs ", int " sendnow );
.fi
.IP
This routine can be invoked only on streams created by
.BR xdrrec_create ().
The data in the output buffer is marked as a completed record,
and the output buffer is optionally written out if
.I sendnow
is nonzero.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdrrec_eof(XDR *" xdrs );
.fi
.IP
This routine can be invoked only on streams created by
.BR xdrrec_create ().
After consuming the rest of the current record in the stream,
this routine returns one if the stream has no more input,
zero otherwise.
.PP
.nf
.BI "bool_t xdrrec_skiprecord(XDR *" xdrs );
.fi
.IP
This routine can be invoked only on
streams created by
.BR xdrrec_create ().
It tells the XDR implementation that the rest of the current record
in the stream's input buffer should be discarded.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_reference(XDR *" xdrs ", char **" pp ", unsigned int " size ,
.BI "                     xdrproc_t " proc );
.fi
.IP
A primitive that provides pointer chasing within structures.
The argument
.I pp
is the address of the pointer;
.I size
is the
.I sizeof
the structure that
.I *pp
points to; and
.I proc
is an XDR procedure that filters the structure
between its C form and its external representation.
This routine returns one if it succeeds, zero otherwise.
.IP
Warning: this routine does not understand null pointers.
Use
.BR xdr_pointer ()
instead.
.PP
.nf
.BI "xdr_setpos(XDR *" xdrs ", unsigned int " pos );
.fi
.IP
A macro that invokes the set position routine associated with
the XDR stream
.IR xdrs .
The argument
.I pos
is a position value obtained from
.BR xdr_getpos ().
This routine returns one if the XDR stream could be repositioned,
and zero otherwise.
.IP
Warning: it is difficult to reposition some types of XDR
streams, so this routine may fail with one
type of stream and succeed with another.
.PP
.nf
.BI "bool_t xdr_short(XDR *" xdrs ", short *" sp );
.fi
.IP
A filter primitive that translates between C
.I short
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "void xdrstdio_create(XDR *" xdrs ", FILE *" file ", enum xdr_op " op );
.fi
.IP
This routine initializes the XDR stream object pointed to by
.IR xdrs .
The XDR stream data is written to, or read from, the
.I stdio
stream
.IR file .
The argument
.I op
determines the direction of the XDR stream (either
.BR XDR_ENCODE ,
.BR XDR_DECODE ,
or
.BR XDR_FREE ).
.IP
Warning: the destroy routine associated with such XDR streams calls
.BR fflush (3)
on the
.I file
stream, but never
.BR fclose (3).
.PP
.nf
.BI "bool_t xdr_string(XDR *" xdrs ", char **" sp ", unsigned int " maxsize );
.fi
.IP
A filter primitive that translates between C strings and
their corresponding external representations.
Strings cannot be longer than
.IR maxsize .
Note:
.I sp
is the address of the string's pointer.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_u_char(XDR *" xdrs ", unsigned char *" ucp );
.fi
.IP
A filter primitive that translates between
.I unsigned
C characters and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_u_int(XDR *" xdrs ", unsigned int *" up );
.fi
.IP
A filter primitive that translates between C
.I unsigned
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_u_long(XDR *" xdrs ", unsigned long *" ulp );
.fi
.IP
A filter primitive that translates between C
.I "unsigned long"
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_u_short(XDR *" xdrs ", unsigned short *" usp );
.fi
.IP
A filter primitive that translates between C
.I "unsigned short"
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_union(XDR *" xdrs ", enum_t *" dscmp ", char *" unp ,
.BI "                 const struct xdr_discrim *" choices ,
.BI "                 xdrproc_t " defaultarm ");     /* may equal NULL */"
.fi
.IP
A filter primitive that translates between a discriminated C
.I union
and its corresponding external representation.
It first
translates the discriminant of the union located at
.IR dscmp .
This discriminant is always an
.IR enum_t .
Next the union located at
.I unp
is translated.
The argument
.I choices
is a pointer to an array of
.BR xdr_discrim ()
structures.
Each structure contains an ordered pair of
.RI [ value , proc ].
If the union's discriminant is equal to the associated
.IR value ,
then the
.I proc
is called to translate the union.
The end of the
.BR xdr_discrim ()
structure array is denoted by a routine of value NULL.
If the discriminant is not found in the
.I choices
array, then the
.I defaultarm
procedure is called (if it is not NULL).
Returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_vector(XDR *" xdrs ", char *" arrp ", unsigned int " size ,
.BI "                  unsigned int " elsize ", xdrproc_t " elproc );
.fi
.IP
A filter primitive that translates between fixed-length arrays
and their corresponding external representations.
The argument
.I arrp
is the address of the pointer to the array, while
.I size
is the element count of the array.
The argument
.I elsize
is the
.I sizeof
each of the array's elements, and
.I elproc
is an XDR filter that translates between
the array elements' C form, and their external
representation.
This routine returns one if it succeeds, zero otherwise.
.PP
.nf
.BI "bool_t xdr_void(void);"
.fi
.IP
This routine always returns one.
It may be passed to RPC routines that require a function argument,
where nothing is to be done.
.PP
.nf
.BI "bool_t xdr_wrapstring(XDR *" xdrs ", char **" sp );
.fi
.IP
A primitive that calls
.B "xdr_string(xdrs, sp,MAXUN.UNSIGNED );"
where
.B MAXUN.UNSIGNED
is the maximum value of an unsigned integer.
.BR xdr_wrapstring ()
is handy because the RPC package passes a maximum of two XDR
routines as arguments, and
.BR xdr_string (),
one of the most frequently used primitives, requires three.
Returns one if it succeeds, zero otherwise.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR xdr_array (),
.BR xdr_bool (),
.BR xdr_bytes (),
.BR xdr_char (),
.BR xdr_destroy (),
.BR xdr_double (),
.BR xdr_enum (),
.BR xdr_float (),
.BR xdr_free (),
.BR xdr_getpos (),
.BR xdr_inline (),
.BR xdr_int (),
.BR xdr_long (),
.BR xdrmem_create (),
.BR xdr_opaque (),
.BR xdr_pointer (),
.BR xdrrec_create (),
.BR xdrrec_eof (),
.BR xdrrec_endofrecord (),
.BR xdrrec_skiprecord (),
.BR xdr_reference (),
.BR xdr_setpos (),
.BR xdr_short (),
.BR xdrstdio_create (),
.BR xdr_string (),
.BR xdr_u_char (),
.BR xdr_u_int (),
.BR xdr_u_long (),
.BR xdr_u_short (),
.BR xdr_union (),
.BR xdr_vector (),
.BR xdr_void (),
.BR xdr_wrapstring ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH SEE ALSO
.BR rpc (3)
.PP
The following manuals:
.RS
eXternal Data Representation Standard: Protocol Specification
.br
eXternal Data Representation: Sun Technical Notes
.br
.IR "XDR: External Data Representation Standard" ,
RFC\ 1014, Sun Microsystems, Inc.,
USC-ISI.
.RE
.SH COLOPHON
This page is part of release 5.13 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
